1. Technical Field
The inventions relate to apparatus for DSL communications and methods of operating such apparatus.
2. Discussion of the Related Art
This section introduces aspects that may be helpful to facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Many digital subscriber loop (DSL) communication systems are susceptible to downlink and/or uplink crosstalk between the links connecting pairs of DSL transceivers that communicate over the links. The crosstalk is typically caused by physical effects such as inductive coupling between the twisted wire pairs of common local-end lines of the telephone company. Such crosstalk can negatively affect communications by reducing distances over which DSL data communications can be maintained and/or by reducing maximum DSL data communication rates.
Some multi-channel data communication systems compensate for undesired effects of crosstalk in downlink and uplink communications. To perform such compensation, the multi-channel data communication systems typically measure downlink and uplink channel matrices, i.e., HD and HU, respectively, for the shared communications channel. From the form of the downlink channel matrix, HD, a central transmitter may precode downlink multi-channel data communications so that far-end transceivers receive data signals that are substantially free of crosstalk-related distortions. From the uplink channel matrix, HU, a central receiver may decode received uplink multi-channel data communications to produce separated data signal streams that are substantially free of crosstalk-related distortions.
The measurement of the downlink and uplink channel matrices HD and HU may be performed during initialization and/or tracking of the parallel multi-channel data communication sessions over the multi-channel communication system. In addition, different pairs of channel matrices HD and HU may be measured for different frequency channels or disjoint sets of frequency channels, e.g., different DSL tones or disjoint sets of nearby DSL tones. The measured forms of the downlink and uplink channel matrices HD and HU may be updated as data communication sessions are added to or removed from the set of parallel DSL communication that share the communications channel. The compensation of a set of simultaneous communication sessions on different channels to reduce undesired effects of crosstalk there between is referred to as vectoring. Such vectoring may be done to reduce crosstalk between the DSL data communication sessions carried by a group of local-end lines that suffer from inter-line inductive coupling. Such of a group of DSL communications sessions that undergo DSL vectoring will be referred to as a DSL vectoring group.